EP0890117B1 - Device and process for determining position - Google Patents

Abstract

A device for determining the position of objects (T) inside a space (P), in particular for locating a tumor inside a human body. At least one emitter unit (SE) and at least one receiver unit (S11, . . . S22) are provided and, in a first embodiment, the emitter unit(s) (SE) are located inside and/or as close as possible to the object (T) under observation and the receiver units(s) (S11, . . . S22) are located preferably outside the space (P). In a second embodiment, the receiver unit(s) (SE) are located inside and/or as close as possible to the object (T) under observation and the emitter unit(s) (S11, . . . S22) are located preferably outside the space (P).

Description

The present invention relates to a device according to the preamble of claims 1 and 2, use the same as well as a method according to the preamble of Claims 15 and 16.

With numerous technical and medical processes are information about the position of an object from of greatest importance. Meanwhile in medicine the position of individual tissue parts - for example a tumor, irradiated to destroy or limit growth to be determined - must be determined Position detection for input into a computer system, for example for "Cyber Space" applications from general meaning. Such a position detection or. Position entry unit is used in these applications also referred to as a three-dimensional mouse. In this Reference is made to the documents US-4 737 794, US-4 945,305 and U.S. 5,453,686.

A medical application is - as mentioned - in the treatment of tumors in the human body, wherein the tumor with photons or in special cases also with Proton rays is irradiated. The goal is one such radiation treatment that only the tumor forming tissue part is irradiated. The one surrounding the tumor Tissue should be damaged as little as possible become. One tries to achieve this requirement by by the dose distribution of the applied radiation is adjusted as precisely as possible to the tumor volume the location of the tumor is limited.

Different methods are available for both photons also known for proton radiation, some of which significant quality differences between the different Methods exist. With all of these known methods, under- Avoid damage to healthy tissue - provided that once diagnosed Tumor position remains constant over the treatment period.

In the treatment of stationary tumors have been partial achieved considerable success. So in particular Treatment of fundus melanoma with Proton beams have proven to be extremely successful.

In contrast, tumors in the chest and abdomen are in the general not fixed. Your position will rather be through natural movements, such as through breathing, heart contractions, peristalsis, etc., constantly changing.

Treatment success similar to that of fixed should be Tumors are reached, so the position of the tumor be known exactly during the irradiation.

In an article by K. Ohara et al. with the title "Irradiation Synchronized with Respiration Gate" (International Journal on Radiation Oncology Biology Physics, 1989, vol. 17, pages 853 to 857) therefore a real-time simulation of the tumor position proposed, the basis of the simulation being the Deformation of the body surface, especially the Deformation due to breathing movement was used. The However, method has inaccuracies because it is on the one hand, not a direct measurement of the tumor position it's just an indirect measurement, and there on the other hand, the other position-determining factors such as Heart contraction and bowel movement - not taken into account become.

WO 94/04938 describes a device for determining the position known, with several transmitter units and one Receiving unit are provided. With the help of the transmitter units Dipole fields are generated - staggered in time, which are received with the receiving unit. Due to the received signals becomes the position of the receiving unit certainly.

The known teaching has the disadvantage that the Measuring accuracy especially with small dimensions for the receiving unit is insufficient.

The present invention is therefore based on the object based on specifying a device in which the position of objects can be determined more precisely.

This task is carried out in the characterizing part of the Claims 1 and 2 specified measures and the method specified in claims 15 and 16 solved. Advantageous embodiments of the invention and a use the same are specified in further claims.

With the help of the device according to the invention, the The position of an object in the room is very precisely determined become. In addition, the position can be determined without direct connection to the object.

Will be on the tumor or on a near the tumor located tissue part a miniaturized, signals emitting transmission unit attached, then by the Receive these signals outside the body with the help of Receiving units precisely the position of the tumor at all times be calculated. Analogously, the Position determination can also be made in that the receiving unit in or at the tumor and the transmitting unit or transmitter units are placed outside the body. The latter arrangement also has the advantage that the body has a lower transmission power and therefore is exposed to less thermal stress than in the first method. In addition, the Transfer of the object, i.e. the tumor Outward signals a lot with the latter arrangement easier, because for this transmission a lower one Transmission power must be made available as in the first method.

In the medical application, the near the Object, i.e. of the tumor, positioned unit if this is is necessary through surgery in the Body of the patient implanted. With the first Arrangement is used to send out signals through the Sending unit requires energy either over a outer field to the transmitter unit or via a Wire connection between a generator unit and the Transmit unit. In another embodiment the transmitter unit has its own Energy storage, which is consequently implanted.

The above statements apply to the second arrangement mutatis mutandis, i.e. that the Receiving units received signals over Wire connections are transmitted to the outside. Indeed - as mentioned - this implementation form for the Transmission of the measurement signals requires less energy.

Fig. 1

ein vereinfachtes Funktionsblockschaltbild der erfindungsgemässen Vorrichtung,

Fig. 2

einen Aufbau einer als Empfangseinheit in der erfindungsgemässen Vorrichtung verwendeten Induktionsspule und

Fig. 3

eine weitere Ausführungsform der Induktionsspule gemäss Fig. 2.

The invention is explained in more detail below with reference to drawings, for example. It shows

Fig. 1

a simplified functional block diagram of the device according to the invention,

Fig. 2

a structure of an induction coil used as a receiving unit in the device according to the invention and

Fig. 3

a further embodiment of the induction coil according to FIG. 2.

Fig. 1 shows a human body P one with the Device to be treated according to the invention. The device according to the invention consists of a Transmitter unit SE, a generator unit GE, a hose SL, receiving units S11 to S22, one Signal processing unit SA, a computing unit RE and an irradiation unit BE.

As mentioned at the beginning is knowledge of the exact position of a tissue part T to be irradiated, for example one Tumor, an essential requirement for a maximum Protection of the healthy tissue adjacent to the tumor. For this position determination, the miniaturized transmitter unit SE as close as possible, preferably positioned directly next to the tumor so that the Sending unit SE, if possible, all movements related to exposed tissue part T experiences, also participates.

One way to send the transmitter unit SE at the desired location in Positioning bodies consists of using a Puncture hollow needle, with the help of the SL tube from the body surface is led to the tissue part T. By this hose SL is the transmitter unit SE in the Tissue part T or brought in the vicinity of the tissue part T.

The tissue part T to be irradiated is located on the Body surface or near a natural one Body cavity, so is the transmitter unit SE of course to fix on the body surface or the If possible, the transmission unit is a natural one Body opening in the relevant body cavity introduce without having to penetrate tissue, such as for example when using a Puncture hollow needle is the case.

If the position determination according to the invention is used in order to be able to irradiate a tissue part T, for example a tumor, the computing unit RE is operatively connected to the radiation unit BE. The irradiation unit BE can thus act precisely on the tissue part T based on the position information of the computing unit RE, two basic possibilities of the irradiation process being conceivable:
On the one hand, it is conceivable that a target area, in which the rays develop their full effect, is tracked to the moving and irradiating tissue part T or, on the other hand, that the irradiation is only carried out when the tissue part T is in the predetermined target area.

In the already mentioned and shown in Fig. 1 Embodiment of the invention is the energy supply the transmitter unit SE via a through the hose SL guided connection cable VK, which to the generator unit GE on one side and to the transmitter unit SE on the other side is connected.

However, it is also conceivable that the transmitter unit SE has one Energy storage, for example in the form of a battery, or that the transmitter unit SE by one through the Generator unit GE generated electromagnetic field is excited. These two embodiments have the Advantage that no connecting cable VK between the Generator unit GE and the transmitter unit SE are necessary, with which a field broadcast by the transmission unit SE, the is used to determine the position, is not disturbed. In addition, the transmitter unit SE can between individual Treatments are left in the body. The disadvantage is however - especially in the embodiment with the in the transmitter unit SE integrated energy storage - the resulting larger transmission unit SE what particularly disruptive when implanted in the body can be.

The transmitter unit SE is used for a electromagnetic field, represented in FIG. 1 by to build individual field lines FL, that of the Receiving units S11 to S22, which are preferably outside of the body P are arranged, can be received. Though represents a human body P in terms of Propagation properties of electromagnetic waves in the different tissues represent a very inhomogeneous medium, however, influencing one is the body P penetrating magnetic field negligible. For this This is because the preferred embodiment is in the body P placed transmitter unit SE from a miniaturized Coil, a magnetic field emanating from this coil corresponds to a magnetic dipole. Do you know that magnetic moment and the location of a dipole in space, so is the strength of the magnetic field at every point in space calculable, whereby the values for the magnetic field strength by the three Cartesian coordinates x, y, z, the polar angle  and the azimuth  of the dipole are clearly determined. The magnetic moment of a dipole can be calculated or by suitable measurements are determined.

The position of the dipole in space, as in the present application is required, the inverse represents Problem, namely based on the measurements of the Field strengths of the field emitted by the dipole is the Position of the dipole determined.

A complete position determination requires that Knowledge of the magnetic moment of the transmitter unit SE or the transmitter coil contained in the transmitter unit SE and the Measurement of at least five linear independent Derivatives of their magnetic field.

A possible method for determining the position of a magnetic dipoles in space is described in the article by W. M Wynn et al. entitled "Advanced Superconducting Gradiometer / Magnetometer Arrays and a Novel Signal Processing Technique "(IEEE Transactions of Magnetics, Vol. MAG-11, No. 2, March 1975, pages 701 to 707). However, with this known method Position determination based on a dipole in which the magnetic moment is unknown. For this reason in addition to the field derivatives, a component of the Magnetic field can be measured.

When using this method on the inventive However, the magnetic moment can be taught in one of them Measurements to determine position independent measurement be obtained, i.e. on the measurement of the field component there is no need for positioning.

To measure the field derivatives (field gradients) are the Receiving units S11 to S22 are provided, each two of these receiving units, namely S11 and S12 and S21 and S22, used to determine a field derivative become. For the sake of simplicity, only those are shown in FIG four receiving units S11 to S22 are shown. Indeed a total of ten receiving units are necessary for the five variables x, y, z,  and  can be clearly determined can. However, to check the measured values also provided more than ten receiving units with which redundant information is obtained due to which the accuracy of the measurements can be assessed.

As receiving unit S11 to S22 are preferred Induction coils used. The induction coils integrate the magnetic flux within their Volume. This magnetic flux can then be used to Determine the mean magnetic field strength in the coil volume. However, one is at the position determination Field strength interested in a point in space.

From the publication entitled "Experimental Methods in Magnetism" by EP Wohlfarth (Volume 2, Chapter 1, pages 2 to 7) it is known that, if the coil dimensions are chosen appropriately, the measured value that the coil delivers can be achieved with only a small amount Deviations corresponds to the value of the magnetic field strength, namely in the center of the coil. This can be expected in particular if the ratio of length to diameter of the induction coil used is calculated using the following formula: ζ ρ 2 = 3 20 · 1 - γ 5 1 - γ 3 in which γ = ρ 1 ρ 2 and ρ ₁ , ρ _{2 is} the inner and outer diameter of the induction coil. It has recently been shown that - if γ <0.3 - a fourth-order component is smaller than 2 x 10 ^-3 and thus exerts a smaller influence than the magnetic induction B _z along the axis of symmetry of the induction coil.

As already mentioned, two of the Receiving units S11 to S22 for determining the Derivatives (gradients) of the magnetic field together connected. For this purpose, the signal processing unit SA Amplification units D1 and D2 with two inputs each provided, at each input a receiving unit S11 up to S22 or an induction coil is connected. It it is again pointed out that for a Position determination in the room a correspondingly larger one Number of amplification units must be available as this can be seen in Fig. 1, because in Fig. 1 only two for the sake of clarity Amplification units D1 and D2 or only four Receiving units S11 to S22 shown.

In the amplification units D1 and D2 the Magnetic field difference between the two at the inputs pending signal values are formed. This Magnetic field difference becomes the derivative of the magnetic field approximately equated.

Because of the miniaturization, especially one as a coil trained transmitter unit SE, is the generated Magnetic field strength very small. With that, others pose Magnetic field sources, such as those not specifically shielded Spaces can be a problem. For this reason becomes a in the signal processing unit SA narrow band filtering and / or phase sensitive Reinforcement in the amplification units D1 and D2 received signal values made. So a big one Part of the unwanted signal components, including noise, be eliminated. They also contribute to the determination the derivatives of the magnetic field (gradient) are required Differences in the amplification units D1 and D2 to reduce interference.

The induction coils must be very homogeneous and reproducible be wound so that of the induced in the coil Voltage with high accuracy on the magnetic field strength can be closed. The homogeneity and Reproducibility are common with conventional windings Round copper wire is extremely difficult to reach. Out for this reason, two more options are below proposed for the realization of induction coils at which the disadvantages mentioned above are avoided.

First of all, let's start with the one already mentioned Device according to the invention explained, which differs from the distinguishes only in that broadcast and Receiving units are exchanged, with which a so-called Differential field due to the measurement of the field derivative interconnected coils, which are now one given current are flowing through. So is in this embodiment, the receiving unit or Receiving units in or near the object T - i.e. of the tumor - and the transmitter unit or transmitters outside the room K - i.e. of the body - positioned. This embodiment has the advantage that the outside of the body K lying higher lying units May have performance limits than the first mentioned variant. This will result in the receiving unit achieved a significantly improved signal-to-noise ratio, with which the requirements for the measurement signals processing arithmetic unit are smaller and what the Measurement results become more accurate. In addition, the receiving unit placed at the object much smaller Amounts of energy to transmit the measurement signals to the outside, which in most cases is battery-powered or receiving unit based on a transponder principle is sufficient.

To further improve the accuracy of the measurement signals, are several calibration coils with known positions provided on the basis of which disturbance variables are recorded, the when determining the position in a corrective manner be used.

In this second variant, the Positioning both a time and a Frequency division multiplex method applicable: Time division multiplexing sends only one transmission unit at a time - if a difference field is sent, the two corresponding transmission units S11 and S12 or S21 and S22 - in a defined period of time. At the Frequency division multiplexing, however, all send Sending units simultaneously, but with defined, different from other differing frequencies.

In the aforementioned second embodiment of the Invention is illustrated by that in FIG. 1 Configuration started, with sending and receiving location were exchanged. However, one is also conceivable Design variant in which in the receiving unit SE For example, two coils are provided with which either absolute values or field derivatives are measured. The same applies to the transmission units S11 to S22, each designed as a coil or as a pair of coils can.

For the determination of the exact position be on the essay by S. Kirsch et. al. titled "Real Time Tracking of Tumor Positions for Precision Irradiation "(Proceedings of the Second Symposium on Hadrontherapy, September 9-13, 1996).

In the following, two further options for realizing induction coils are discussed, which make it possible to determine the voltages induced in the coils with high accuracy:
A first embodiment of the induction coil is shown in FIG. 2, with a foil F, which is coated with parallel copper strips KS, being used instead of a wire. The film width corresponds to the desired winding length and thus the length of a bobbin SK to be wound. As shown in FIG. 2A, the film F is wound directly onto the coil former SK, the entire wire layer of a conventional induction coil corresponding to a film layer. 2B shows how the parallel copper strips KS are connected to one another via an electrical connecting line EL. In this case, the end of a copper strip KS located at the start of the winding WA must be connected to an end of a copper strip KS located at the winding end WE, which, however, requires a relatively complicated connection technique.

For this reason, in the case where only that Differential signal from two induction coils is required improved the induction coil just explained in that that the application of the above connection technology can be avoided. As mentioned, the present application (gradiometer), namely measuring of field derivatives (field gradients), only that Difference signal from two induction coils of interest. Because of this limitation, the winding can to be simplified by both Induction coils are made from the same film F. This is illustrated with reference to FIG. 2C, from which it can be seen is that the film F at the winding start WA twice is folded at right angles. Furthermore, both Induction coils in parallel on the same bobbin wound. This ensures that the same Copper strips once from the outside in and for them second induction coil is guided from the inside to the outside. This is an induced in the first induction coil Reverse polarity signal also in the second Induction coil induces, with which the same signals compensate each other. It follows that at the Connection points AS1 and AS2 in the in Fig. 2C embodiment shown only the difference signal pending. The explained with reference to Fig. 1 and as Differential amplifier trained amplification units D1 and D2 are no longer necessary in this case.

As a major advantage of those explained with reference to FIG. 2C Induction coils compared to those explained with reference to FIG. 2A Induction coils is that no additional electrical Connection lines between the winding start WA and the winding end WE are necessary, because are now located all necessary connections at the winding end WE (Fig. 2C).

Another embodiment of the invention Induction coils is in Fig. 3 or in Figs. 3A and 3B shown, the in this embodiment Induction coils are constructed from foil disks FS preferably by means of a photolithographic Process either a left or a right turn Copper spiral KSPL or KSPR are applied (Fig. 3A). ever one of these left-handed copper spirals KSPL is included a clockwise rotating copper spiral KSPR each inside Spiral start via an electrical connection line EL connected. This ensures that the sense of rotation of the copper strip from the outer beginning of the left-turning Spiral to the outer end of the clockwise spiral does not change. This means that the induced Add signals. The induction coil is now one Stack of such left and right rotating pairs of spirals corresponding to the arrangement shown in Fig. 3B built up, the spiral pairs only electrically on the outside need to be connected.

The induction coils explained with reference to FIGS. 2 and 3 can be used in any application in which Magnetic field components or their derivatives determined Need to become. Especially when high accuracy of sizes to be measured and a high sensitivity of the Unit of measurement is required, the specified ones are suitable Induction coils especially as gradiometers. Furthermore the induction coils designed in this way are crowding downright for the determination of small magnetic field components or their derivatives, because small values can with these induction coils can be measured very precisely. It also ensures simple manufacture such induction coils an extremely good one Reproducibility of the measured sizes with different Induction coils.

Since the used as receiving unit S11 to S22 Induction coils only on time-changing fields respond, the trained as a transmitter unit SE Transmitter coil with a time-variable current signal from known shape and size.

However, others can also be used as the receiving unit S11 to S22 Sensors can be used as induction coils. Is conceivable in particular the use of SQUID ("Sensors", W. Göpel et al. Publisher VC Hauer, Weinheim, 1989).

The position determination of a transmitter unit SE by measurement of the modulated field it generates using Gradiometers is not limited to that Position determination of tumors to be irradiated. Much more the device according to the invention can be found anywhere there use successfully where a non-contact Positioning is needed.

In the illustrated embodiment with a Sending unit for the object whose position is to be determined in a further development it is conceivable that further Sending units at the respective object or other locations be placed. So that with the receiving units multiple positions can be determined. However, it must make sure that the transmitter units are either in different time periods (time division multiplexing) or with different frequencies (frequency division multiplexing) send.

In a similar way, the embodiment variant, is of a receiving unit in or near the object is intended to be further developed such that further Receiving units in or near the object or on other places are provided. Advantageous with this Embodiment is that the positions of the different receiving units can be determined simultaneously can, since neither a time division nor a Frequency division multiplexing is necessary.

The device according to the invention was based on a medical application explained in detail. This will however, the universality of the invention in no way limited. So the invention is suitable Device in particular as a so-called three-dimensional Mouse in "Cyber Space" applications or the like.

Claims (16)

1. Device for determining the position of an object (T) in a space (P), in particular for determining a tumour in a human body, where several receiver units (S11, ..., S22) and a transmitter unit (SE) are provided, characterised in that at least two receiver units (S11, ...., S22) are provided for each parameter to be determined which corresponds to a degree of freedom of the transmitter unit (SE), that the two receiver units (S11, ...., S22) required to determine such a parameter arc connected together to measure a field gradient, where the transmitter unit (SE) is positioned in or as close as possible to the object to be observed (T) and the receiver units (S11, ....., S22) are preferably positioned outside the space (P).
2. Device for determining the position of an object (T) in a space (P), in particular for determining a tumour in a human body, where several transmitter units (S11, ...., S22) and a receiver unit (SE) are provided for sending and receiving a magnetic field. characterised in that two transmitter units (S11, ....., S22) are provided for each parameter to be determined which corresponds to a degree of freedom of the receiver unit (SE), that the two transmitter units (S11, ....., SE22) required to determine such a parameter are connected together to generate a differential field, where the receiver unit (SE) is positioned in or as close as possible to the object to be observed (T) and the transmitter units (SE11, ....., SE22) are preferably positioned outside the space (P).
3. Device according to claim 1 or 2, characterised in that the transmitter unit (SE; S11, ....., S22) and/or the receiver unit (SE11, ....., SE22; SE) have an energy accumulator.
4. Device according to claim 1 or 2, characterised in that a generator unit (GE) is provided outside the space (P), where the generator unit (GE) is actively connected with the transmitter unit or receiver unit (SE) positioned inside the space (P).
5. Device according to any of the previous claims, characterised in that at least one calibration coil with known position is provided to calibrate the measurement results.
6. Device according to any of the previous claims, characterised in that the receiver units (SE; SE11, ....., SE22) are formed as induction coils, that the windings of the induction coils are formed as parallel electrically conductive strips (KS) applied to a film (F) and that the ends of the parallel strips (KS) are connected to windings by means of electrical connecting leads (EL).
7. Device according to claim 6, characterised in that the film (F) is folded twice to form two interconnected identical induction coils.
8. Device according to any of claims 1 to 5, characterised in that the receiver units (SE; SE11, ....., SE22) are formed as induction coils, that the induction coils consist of several film discs (FS) and that electrically conductive spirals (KSPL, KSPR) are applied to the film discs (FS).
9. Device according to claim 8, characterised that in each case a right- and a left-turning spiral (KSPL, KSPR) are connected together electrically at the inner spiral ends into a spiral pair and that the spiral pairs are connected together at the outer spiral ends.
10. Device according to any of claims 1 to 5, characterised in that the receiver units (SE; SE11, ....., SE22) are formed as magnetic field sensors, in particular of the SQUID type.
11. Device according to any of the previous claims, characterised in that a signal preparation unit (SE) and a computer unit (RE) are provided which are exposed to the signals from the signal preparation unit (SA) measured by the receiver units (SE; SE11, ....., SE22) and the signals prepared in the signal preparation unit (SE) from the computer unit (RE) to determine the position.
12. Device according to any of the previous claims, characterised in that an irradiation unit (BE) is provided to irradiate the object (T).
13. Device according to claim 12, characterised in that the irradiation unit (BE) can be guided according to the object (T) or that the irradiation unit (BE) is activated only when the object (T) is in a fixed prespecifiable target area.
14. Use of the device according to any of claims 1 to 11 for three dimensional position input units.
15. Process for determining the position of an object (T) in a space (P), in particular for determining a tumour in a human body, where the process comprises:

    at least one transmitter unit (SE) is positioned in the object (T) or as close as possible to the object (T),

    the transmitter unit (SE) generates an electromagnetic field, preferably a magnetic field, and

    the position of the transmitter unit (SE) is determined from field gradient measurements.
16. Process for determining the position of an object (T) in a space (P), in particular for determining a tumour in the human body, where the process comprises:

    at least one receiver unit (SE) is positioned in the object (T) or as close as possible to the object (T),

    at least two transmitter units (SE11, ....., SE22) lying outside the space (P) generate a magnetic differential field and

    the position of the receiver unit (SE) is determined on the basis of measurements of the electromagnetic field in the receiver unit (SE).

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